It is common for people to listen to music with a music player via ear plugs. Listening to music is a one way of relaxing oneself and to improve the mental condition of the listener, for example. Moreover, people are nowadays applying various other methods to improve the physical or mental condition as well. One may seek the improvement from traditional means, such as exercise or sleep, while another relies in more technical means, such as receiving optical radiation from an optical treatment device. However, it may happen that these methods are mutually excluding.